1. Field of the Invention
The present invention relates to a drill including a stem having a shank at one of its ends and at least two discharge grooves for discharging drilling dust and helically circumscribing the stem, and a drill head provided at an end of the stem opposite the end provided with the shank, with the drill head being provided with bits, which are formed of hard metal and project radically beyond the drill head, and with a plurality of drilling dust grooves which are located between the bits and the number of which exceeds the number of the discharge grooves, with at least one pair of the drilling dust grooves passing into a common discharge groove.
2. Description of the Prior Art
For forming bores in concrete, brickwork, stone and the like, drills having drill heads with bits formed of a cutting material, preferably, hard material, are used. The drills are usually inserted in a hand-held drilling tool which in addition to a rotary drive includes a hammer mechanism for imparting axial blows to the drill. The axial blows are imparted to a shank provided at the end of the drill stem and which is received in the drilling tool chuck, and are transmitted through the stem and drill head to a structural component in which a bore is drilled. In this way, the structural component is shaved, chiseled, and is subjected to a treatment which is accompanied by chip removal. The drill, in addition to meeting requirements with respect to drill feed and an necessary expenditure of force, should have as long as possible service life.
Prior art discloses a number of drills which are characterized, under normal operational conditions, by satisfactory feed characteristics and force expenditures. Also under normal operational conditions, their service life is also acceptable. Such a drill is disclosed, e.g., in U.S. Pat. No. 4,903,787. The drill has a stem with a shank adapted to be received in a hand-held tool, and a drill head provided at a stem end opposite the shank. The drill head has four bits which are provided in a star-shaped insert formed of a hard material. The bits are separated by drilling dust grooves which open in two discharge grooves for discharging the drilling dust and which helically circumscribe the stem. The known drill is capable of meeting the necessary requirements, in particular of a professional user, at small and medium bore diameters. However, for the use of the drill for drilling large diameter bore, it needs improvement. In particular, during drilling a bore in a reinforced concrete, the drill can encounter a reinforcing metal and be hooked over the reinforcing metal. The danger of a drill head being hooked over the reinforcing metal increases with an increase of a diameter of a to-be-drilled bore.
Accordingly, an object of the present invention is to eliminate the drawbacks of the prior art drills and provide a drill with which a danger of the drill being hooked during drilling bores in a reinforced concrete is reduced even during drilling bores having a large diameter.
Another object of the present invention is to provide a drill having good feed characteristics at a reduced expenditure of force, and having an increased service life.
These and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a drill, in particular a rock drill including a stem having a shank at one of its ends and at least two discharge grooves for discharging drilling dust and helically circumscribing the stem. At its opposite end, the stem is provided with a drill head having bits which are formed of hard metal and project radically beyond the drill head. A plurality of drilling dust grooves separates the bits, and their number exceeds a number of the discharge grooves, into which they open. At least one pair of the drilling dust grooves passes into a common discharge groove. A helical groove section forms a common transitional region between the at least one pair of the drilling dust grooves and the common discharge groove. The helical groove section has a passing cross-section which is smaller than the passing cross-section of the common discharge groove.
The helical groove section which, according to the present invention, connects two drilling dust grooves opening in a common discharge groove counteracts the tendency of the drilling head to hook over the reinforcing metal. In a drill, e.g., with three bits and three drilling dust grooves separating the bits, one of the drilling dust groove opens directly into an associated discharge groove. In the conventional drills, the bit which, viewing in a rotational direction, is located immediately in front of a drilling dust groove, which opens directly into a discharge groove, is supported axially only by a small amount of the drill head material as a relatively large width of the helical groove section occupies a relatively large portion of the axial width of the discharge groove. According to the invention, the helical groove section has a noticeably smaller passing cross-section. Therefore, a longer web remains under the circumferential bit which forms a head side limiting shoulder of the helical groove section. This advantageously favors the drill advance. Upon encountering a reinforcing metal, in particular during drilling the metal, the danger of hooking of the shorter material web behind the metal is reduced.
The smaller passing cross-section of the helical groove section is preferably achieved by providing, at a same root diameter of the stem a helical groove section having a smaller opening width than the opening width of the common charge groove measured over the drill circumference. The root diameter here is the stem diameter at the base of the common discharge groove. Providing the same root diameter reduces the weakness of the head region of the stem to a most possible extent.
In order to further improve the guide characteristics of the drill in a bore and to increase resistance to hooking, the limiting shoulder of the helical groove section, which is located closer to the shank, gradually passes into a limiting shoulder of the common discharge groove which is likewise located closer to the shank. In this way, the discrete edge-like transitional regions, which can lead to hooking, in particular upon encountering a reinforcing metal, are eliminated.
When reducing the passing cross-section of the helical groove section, care should be taken not to make it very small as the drillings, which are produced by the associated bit, need be removed and, thus, should be able to pass through the helical groove section. Therefore, advantageously, the passing cross-section of the helical groove section amounts to from about 30% to about 20% of the common discharge groove.
For a rapid discharge of produced drilling, it is advantageous when with an uneven number of the drilling dust grooves, the discharge grooves have different passing cross-sections, with the common discharge groove having a larger passing cross-section. The common discharge groove should provide for removal of drillings produced by two bits. This is taken into account by forming the common discharge groove with a larger passing cross-section.
For a good drill advance with a reduced tendency to hooking upon an encounter with reinforcing metal, the drill according to the present invention is provided with three bits, with each two adjacent bits being separated by a drilling dust groove.
According to a further embodiment of the present invention, the drill can have an even number of bits, e.g., four, which are separated by respective drilling dust grooves. The drilling dust grooves open pairwise in respective discharge grooves. In this embodiment, the drill head is formed symmetrical to a most possible extent which is favorable for a uniform loading of the drill head. In this embodiment, the helical groove sections, which form respective transitional regions between respective pairs of the drilling dust grooves and respective common discharge grooves, have the same passing cross-section.
When in the drill according to the present invention with an uneven number of bits, the helical groove section ends, in axial direction, beneath sections of the drill head located under at least two of the bits and is limited by shoulders which are located at the same cross-section of the drill, the drill head can have a smaller height than the conventional drill heads. With an even number of bits, advantageously, the axial supports of all of the bits have substantially the same length.
From the manufacturing point of view, it is advantageous when the helical groove section and the drilling dust grooves have at least partially the same cross sectional profile.
The bits can be provided on plate-shaped inserts formed of hard metal and insertable in slot-like recesses formed in the end surface of the drill head and be, be, e.g., soldered thereto. In accordance with an alternative embodiment of the present invention, the entire drill head can be formed of hard metal. The hard metal drill head can, e.g., be connected with the stem by friction welding or otherwise be fixedly connected with the stem. The advantage of using a hard metal drill head consists in that in can have almost any arbitrary shape, and its mounting on the stem is made easier.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.